In recent times, communications devices have become among the most impacting technologies in our society. Cellular phones, PDAs, smart phones, personal media players, laptops, navigation devices, mobile TVs, and myriad others have reshaped the way human beings live their personal and working lives. In turn, the field of communications devices continues to exhibit some of the most rapid technological innovation.
Generally, the capabilities of a communications device are limited by the ability of the device to receive large quantities of information and retrieve quality usable data from the information. A device's ability to perform these functions depends on the performance of the device's receiver. The receiver can receive a radio frequency (RF) signal from an antenna or a wire medium and process the signal to produce a signal that can be used by other portions of the device to carry out the device's functions. Significantly, the amplitude and quality of the signals that are received at the receiver may vary drastically. Namely, due to, for example, attenuation, variation in distance between the receiver and the transmitter, fading, and the Doppler Effect the amplitude of signals received at the receiver can fluctuate rapidly and vary by as much as several magnitudes while the signal can exhibit noise and distortion. A well performing receiver needs to extract quality information from both high quality and low quality signals.
More specifically, a device can receive a RF signal at the receiver through an antenna. The signal can then be amplified and conveyed to a mixer where the signal's frequency can be converted from its carrier frequency that defines its channel in the spectrum to a low frequency, such as a baseband or a low-IF frequency. After the down conversion in frequency, the signal can be amplified and filtered in a section of the receiver referred to as the baseband portion to eliminate unwanted components and produce a signal of a desired power. After the baseband portion, the signal can be converted to the digital domain and conveyed to a digital demodulator where it can be further processed to be used by other components in the device to carry out the device's functions.
However, filtering and amplifying the signal in the baseband portion can degrade signal quality. For example, filtering a low power signal can introduce excessive noise and amplifying a high power signal can produce distortion, particularly if there is saturation of components. Furthermore, a signal received at the baseband portion can contain an undesired signal component, such as an adjacent channel, which can be orders of magnitudes more powerful than the desired signal component. Powerful undesired signal components can further complicate the processing of signals in the baseband portion by causing saturation and distortion. Baseband portions in present devices either fail to meet these needs or meet them in an expensive to implement and power inefficient manner. What is needed is a cost effective and power efficient baseband section that is flexible, dynamic, and intelligent to the presence of undesired signal components while exhibiting good noise and linearity performance for all signals.